Add logs for creation and discovery of default files

As 'file not found' logs may be interpreted
as errors, let's add logs for the creation and discovery of
new default config and prefs files.

src/main/java/seedu/address/MainApp.java

@@ -117,6 +117,9 @@ protected Config initConfig(Path configFilePath) {
 
         try {
             Optional<Config> configOptional = ConfigUtil.readConfig(configFilePathUsed);
+            if (!configOptional.isPresent()) {
+                logger.info("Config file not found. Will be starting with a new default config file.");
+            }
             initializedConfig = configOptional.orElse(new Config());
         } catch (DataConversionException e) {
             logger.warning("Config file at " + configFilePathUsed + " is not in the correct format. "
@@ -145,6 +148,9 @@ protected UserPrefs initPrefs(UserPrefsStorage storage) {
         UserPrefs initializedPrefs;
         try {
             Optional<UserPrefs> prefsOptional = storage.readUserPrefs();
+            if (!prefsOptional.isPresent()) {
+                logger.info("Prefs file not found. Will be starting with a new default prefs file.");
+            }
             initializedPrefs = prefsOptional.orElse(new UserPrefs());
         } catch (DataConversionException e) {
             logger.warning("UserPrefs file at " + prefsFilePath + " is not in the correct format. "

src/main/java/seedu/address/commons/util/JsonUtil.java

@@ -60,9 +60,9 @@ public static <T> Optional<T> readJsonFile(
         requireNonNull(filePath);
 
         if (!Files.exists(filePath)) {
-            logger.info("Json file " + filePath + " not found");
             return Optional.empty();
         }
+        logger.info("JSON file " + filePath + " found");
 
         T jsonFile;